header {
  padding: var(--s4) calc(var(--s4) * 2);
  border-bottom: var(--border-width) solid var(--f1-border);
  display: flex;
  align-items: center;
  gap: var(--s4);
  flex-shrink: 0;
}

#app {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.page {
  flex: 1;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.back-btn {
  background: none;
  border: none;
  padding: var(--s1) var(--s2);
}